A prior-art press brake (for example, see Patent Document 1) includes plural upper tool holders 121 as shown in FIG. 7 to FIG. 12 at a lower portion of an upper table to which upper tools are attached in order to replace the upper tools easily.
An upper tool clamper 127 for clamping an upper tool 125 is swingably provided on a holder body 123 of the upper tool holder 121. Then, a drop prevention piece 129 to be engaged with a drop prevention groove 125G of the upper tool 125 is attached to a lower portion of the upper tool clamper 127.
A lower potion of the holder body 123 is formed as an upper tool holding portion 131. The upper tool clamper 127 and the upper tool holding portion 131 clamp and unclamp the upper tool 125. A pusher screw 133 is threaded onto an upper portion of the upper tool clamper 127. An end of the pusher screw 133 is contacted with a pusher 135 that is urged outward by urging elements embedded in the holder body 123. An operating lever 137 is attached to the pusher screw 133 in order to operate rotation of the pusher screw 133.
Stoppers 139A and 139B for restricting the rotation of the operating lever 137 is disposed on a front face of the holder body 123. Each of the stoppers 139A and 139B is set on a rotational path of the operating lever 137 (rotation is restricted), or moved out of the rotational path (rotation is allowed). In addition, urging members 141 for continuously urging the upper tool clamper 127 slightly toward its closing direction are disposed between the holder body 123 and the upper tool clamper 127. Further, a ball plunger 145 to be engaged with an engagement recess 143 formed an upper edge of the upper tool clamper 127 is provided.
According to the above-explained upper tool holder 121, in a state where the operating lever 137 is contacted with the stopper 139A as shown in FIG. 7 and FIG. 8, the upper tool 125 is stiffly pushed onto the upper tool holding portion 131 by the upper tool clamper 127, so that the upper tool 125 is clamped. At this state, the drop prevention groove 125G and the drop prevention piece 129 are engaged with each other. On the other hand, in a state where the operating lever 137 is contacted with the stopper 139B as shown in FIG. 9 and FIG. 10, the upper tool 125 is unclamped. In this state, the drop prevention groove 125G is engaged with an engagement protrusion 127P, so that the upper tool 125 is prevented from dropping off. In addition, the upper tool 125 can slides laterally (along a longitudinal direction of the upper tool 125).
The lower portion of the upper tool clamper 127 can be widely opened by swinging the upper tool 125 in a direction R after rotating the operating lever 137 to pass it over the stopper 139B and then to orient it vertically downward as shown in FIG. 11 and FIG. 12. After opening the upper tool clamper 127, the upper tool 125 can be removed downward. When the lower portion of the upper tool clamper 127 is opened, the engagement recess 143 and the ball plunger 145 are engaged with each other to keep the opened state.